1. Field of the Invention
The present invention relates to a method for forming a metal line of a semiconductor device, and more particularly to a method for forming a metal line of a semiconductor device, capable of preventing step coverage failure of a barrier metal and contact filling failure of CVD tungsten.
2. Description of the Prior Art
A size of cells has been gradually shrunken due to high-integration of semiconductor devices, so a height of a capacitor is gradually increased in order to allow the capacitor to have sufficient capacitance identical to capacitance of a conventional capacitor. For example, in a semiconductor device having a size less than 0.10 μm, the height of the capacitor must exceed 25000 Å. For this reason, a metal contact used for electrically connecting a lower conductive pattern to a metal line typically has a height above 30000 Å.
However, if the height of the metal contact increases even through a sectional area of a contact is reduced due to shrinkage of a cell size, step coverage failure of a barrier metal and contact filling failure of CVD tungsten may occur, causing metal contact failure and deteriorating reliability and a yield rate of semiconductor devices.
In detail, in order to allow the capacitor to have sufficient capacitance, two-stepped oxide layers is formed as an insulating interlayer when fabricating the capacitor, thereby ensuring a dimension for a lower portion of the capacitor. At this time, a BPSG layer or a PSG layer having a high wet etch rate is used for a lower oxide layer and a TEOS layer or a USG layer is used for an upper oxide layer. Thus, the dimension of the lower portion of the capacitor, which may become reduced during a dry etch process, can be enlarged through a wet etch process, thereby allowing the capacitor to have sufficient capacitance.
However, when the barrier metal is deposited at a temperature above 400° C., MOCVD TiN cannot be sufficiently deposited in a metal contact in the vicinity of the BPSG layer or the PSG layer due to out gassing. Accordingly, when tungsten is deposited through the following CVD process, tungsten may react with Ti deposited in the vicinity of the BPSG layer or the PSG layer, thereby causing a volcano phenomenon. For this reason, contact filling failure of tungsten may occur, thereby causing metal contact failure.
FIGS. 1 and 2 are photographic views showing metal contact failure caused by a volcano phenomenon occurring in a lower portion of a metal contact, in which Ti is reacted with WF6 due to step coverage failure of a barrier metal (TiN) so that the volcano phenomenon is created.
In addition, if a single oxide layer is used as an insulating interlayer, a height of the contact becomes increased even through a sectional area of the contact becomes decreased, so step coverage failure of a barrier metal (TiN) may occur, thereby resulting metal contact failure.